Method and apparatus for reducing emissions and/or reducing friction in an internal combustion engine

ABSTRACT

A method and apparatus for reducing at least one of HC, CO, and NO x  emissions from an operating internal combustion engine fueled by hydrocarbon or similar fuels, such as alcohols, wherein a portion of the internal combustion chamber has aluminum and/or titanium containing surfaces coated with a titanium dioxide coating further comprising a dopant in and/or on the adherent titanium dioxide coating.

FIELD OF THE INVENTION

The invention relates to a method and apparatus for reducing at leastone of HC, CO, and NO_(x) emissions from an operating internalcombustion engine fueled by hydrocarbon or similar fuels, such asalcohols, wherein a portion of the internal combustion chamber hasaluminum and/or titanium containing surfaces coated with a titaniumdioxide coating, further comprising a dopant in and/or on the titaniumdioxide coating. The invention also provides reduced friction titaniumdioxide coated engine components and methods of making same.

BACKGROUND OF THE INVENTION

Three major automotive pollutants are carbon monoxide (CO), unburnedhydrocarbons (HC), and oxides of nitrogen (NO_(x)). Gasoline, diesel andother hydrocarbon fuels contain hydrogen and carbon, as do similarorganic fuels, such as alcohol-based fuels. Nitrogen, carbon dioxide andoxygen are all present in air. When air and these types of fuels aremixed and burned in internal combustion chambers, the by-products ofcombustion are partially burned fuel, carbon, carbon dioxide (CO₂),carbon monoxide (CO), and water vapor. Since the combustion process inthe cylinders is rarely, if ever, 100% complete, some unburned fuels,for example hydrocarbons (HC), are left over in the exhaust gases.Oxides of nitrogen (NO_(x)) are also formed and are thought to be causedby high cylinder temperature. If the combustion chamber temperatures areabove 1,371 degrees Celsius, some of the oxygen and nitrogen combine toform NO_(x). In the presence of sunlight, HC and NO_(x) join to formsmog. A great deal of attention has been devoted to reducing internalcombustion engine emissions of HC, CO, and NO_(x).

On many commercially available vehicles, catalytic converter devices areused to convert HC, CO and NO_(x) to N₂, O₂, CO₂ and H₂O. Catalyticconverter devices contain beads or honeycomb substrates, coated with athin coating of platinum, palladium, or rhodium, and mounted in acontainer. They are typically installed downstream of the exhaustmanifold and positioned between the exhaust manifold and the muffler.This means of reducing exhaust emissions has drawbacks. The metals usedto coat the beads/honeycombs are expensive and lose their catalyticactivity over time. Also, the catalytic converter device is typicallylocated outside of the engine compartment underneath the vehicle whereit is subject to damage from road hazards. Urea injection systems foundon some diesel engines using Selective Catalytic Reduction (SCR)catalysts also have drawbacks. Injection of a reducing agent, forexample urea or ammonia is necessary for proper function; thus aurea/ammonia source is required. Also, although urea is the safestreducing agent to store, it requires conversion to ammonia throughthermal decomposition in order to be used as an effective reductant.There is thus a need for alternative or supplemental methods of reducingemissions of HC, CO, and NO_(x).

U.S. Pat. No. 3,697,091 describes bearing faces of ferrous metalcompression and oil control piston rings of internal combustion engineshaving a plasma-applied, bearing face coating which consists essentiallyof about 75-90% aluminum oxide and 10-25% by weight titanium oxide. Aferrous metal piston ring coated with a plasma-applied coating ofalumina and titania along with ferric oxide is disclosed in U.S. Pat.No. 4,077,637. In U.S. Pat. No. 4,115,959, a ferrous metal piston ringcoated with a plasma-applied alumina-titania coating is described whichfurther includes about 10-15% of an alkaline earth metal fluoride. Ringscoated with alumina-titania plasma applied coatings have exhibited atendency to flake or blister during engine operation. Blisters of about1/16″ diameter and 0.0001″ thickness appear in the surface of thecoating which is generally 0.004″ thick. The blister material is thenscuffed off and a loss of coating results. Delamination by blisteringand spalling of portions of the coating is undesirable. Ceramiccontaining organic resin paints have also been used on pistons andcylinders to retain heat inside of the combustion chamber, whichincreases cylinder temperature. A downside of known thermal insulatorsis that high cylinder temperature causes NO_(x) formation.

None of the above-described coatings has shown usefulness in reducingthe amount of HC, CO, and NO_(x) exhaust emissions from internalcombustion engines. In addition, these coatings, including so-calledceramic coatings, thermal spray coatings and plasma assisted coatingsare very expensive and are physically adhered, not chemically bonded tothe surface, which results in adhesion problems, particularly duringtemperature cycling. Thermal spray coatings and plasma assisted coatingswill be understood by those of skill in the art to mean coatingsdeposited by using a hot gas spray or gas plasma spray to carry a powderto a substrate where the powder is physically deposited onto thesubstrate. Also, traditional organic containing skirt coatings have poorwear and temperature resistance when compared to the present invention.

SUMMARY OF THE INVENTION

Applicants have found that coating portions of aluminum and/or titaniumsurfaces of an internal combustion engine and/or portions of the exhaustsystem, e.g. the exhaust manifold, which come in contact with intakeair, fuel/air mix and/or exhaust gases with a titanium dioxide coatingas described herein provides surprising reductions of at least one ofHC, CO, and NO_(x) emitted in downstream exhaust gasses.

One aspect of the invention is a method of reducing concentration of atleast one of HC, CO and NO_(x) in exhaust gasses emitted from anapparatus comprising an operating internal combustion engine, the methodcomprising or consisting of steps of:

-   -   a. determining initial concentration of at least one of HC, CO        and NO_(x) in exhaust gasses emitted from an apparatus        comprising an operating internal combustion engine comprising a        combustion chamber and operating at a selected engine operation        parameter,    -   b. selecting a target concentration, less than the initial        concentration, or a target reduction in the initial        concentration of at least one of HC, CO and NO_(x) for the        selected engine operation parameter of said engine;    -   c. coating portions of internal surfaces of one or more of:        -   i. the combustion chamber,        -   ii. an air-intake passage in communication with the            combustion chamber,        -   iii. an exhaust passage in communication with the combustion            chamber;        -   iv. intake and/or exhaust valves; and        -   v. an exhaust manifold in communication with the exhaust            passage;    -   with a titanium dioxide containing coating to effect the target        concentration or the target reduction of concentration of at        least one of HC, CO and NO_(x) in exhaust gasses emitted from        the apparatus.

Another aspect of the invention is a method to reduce emissions from anapparatus comprising an operating internal combustion engine, saidinternal combustion engine comprising a combustion chamber comprising anair-intake valve and an exhaust gas valve; the method comprisingdepositing an chemically adherent titanium dioxide coating comprising atleast 15 wt % titanium dioxide on a portion of aluminum surfaces of atleast one of:

a portion of surfaces defining the combustion chamber;

an internal surface of an air-intake passage in communication with thecombustion chamber via an air-intake port that is opened and closed bythe intake valve;

an internal surface of an exhaust emission passage in communication withthe combustion chamber via an exhaust gas valve through an exhaust gasport;

the air-intake valve;

the exhaust gas valve; and

an exhaust manifold in communication with the exhaust emission passage;

such that, during operation of said engine, intake air, fuel/air mixtureand/or exhaust gas contact said coating thereby increasing decompositionrate of HC, CO or NO_(x) and/or reducing formation rate of CO or NO_(x)emissions resulting from combustion in the combustion chamber.

In one aspect the coating is applied to one or more of a bowl surface ofthe piston; a crown surface of the piston; surfaces of the intake andexhaust valves, in particular those surfaces in contact with thecombustion chamber; a top surface of the cylinder head exposed to thecombustion chamber, a surface of walls of the cylinder.

In another aspect of the invention the method comprises applying thesurface coating to a top surface of each piston, a surface portion ofeach intake and exhaust valve in contact with the combustion chamber, asurface portion of the cylinder head exposed to the combustion chamber,and a wall surface of the cylinder.

Another aspect of the invention provides an internal combustion enginecomprising:

external surfaces and internal surfaces, said internal surfacescomprising a group of internal surfaces contacted during engineoperation with intake air, fuel/air mix and/or exhaust gases, saidinternal surfaces being located on a combustion chamber, an air intakepassage, an exhaust passage, an exhaust manifold, a valve andcombinations thereof; at least a portion of said group of internalsurfaces being metal selected from aluminum, aluminum alloy, titanium ortitanium alloy; and at least some portions of the metal being coatedmetal surfaces having a coating comprising at least 12 wt % TiO₂, saidcoated metal surfaces positioned such that, during operation of saidengine, intake air, fuel/air mixture and/or exhaust gas contact saidcoating thereby increasing decomposition rate of HC, CO or NO_(x) and/orreducing formation rate of CO or NO_(x) emissions resulting fromcombustion in the combustion chamber.

The engine may further comprise an exhaust system extending from theexhaust manifold to an exhaust pipe wherein at least a portion ofinternal surfaces of the exhaust system being aluminum, aluminum alloy,titanium or titanium alloy coated with said coating.

Another aspect of the invention is an engine comprising a combustionchamber having at least one aluminum, aluminum alloy, titanium ortitanium alloy surface, at least a portion of said surface havingdeposited thereon a coating comprising at least 25 wt % TiO₂ in a layerthickness such that during operation of said engine exhaust gasemissions of HC, CO and/or NO_(x) from the combustion chamber are lessthan said emissions from a like engine having no titanium dioxidecoating on combustion chamber surfaces.

Another aspect of the invention is a method to reduce emissions from anapparatus comprising an operating internal combustion engine, comprisingthe steps of:

determining a state of an engine operating parameter corresponding to anemission value of at least one of HC, CO and NO_(x) emitted from acombustion chamber of an operating internal combustion engine,

determining a target reduction in concentration of at least one of HC,CO and NO_(x) in exhaust gas discharged from the operating internalcombustion engine corresponding to the state of the engine operatingparameter corresponding to the emission value of at least one of HC, COand NO_(x) emitted from the combustion chamber of the operating internalcombustion engine, wherein the concentration of the at least one of HC,CO and NO_(x) is measured at a selected location in a path of theexhaust gas that is downstream from the combustion chamber; and

depositing a titanium dioxide containing coating on a portion ofsurfaces of

a. the combustion chamber;b. an air-intake passage in communication with the combustion chamber;c. an exhaust passage in communication with the combustion chamber;d. intake and/or exhaust valves; and/ore. an exhaust manifold in communication with the exhaust passage;to effect said target reduction.

In one embodiment, determining a state of an engine operating parametercorresponding to an emission value of at least one of HC, CO and NO_(x)emitted from a combustion chamber of an operating internal combustionengine comprises determining a state of one or more of the followingengine operating parameters: engine speed, torque, load, exhaust gasrecirculation (EGR) and indicated mean effective pressure (IMEP).

Another aspect of the invention comprises friction and bearing surfacescomprising surfaces coated with polished titanium dioxide which providea reduction in static and dynamic friction as compared to unpolishedtitanium dioxide coated surfaces and conventional friction reducingcoatings for combustion chambers.

Another aspect of the invention comprises an internal combustion enginecomprising:

external surfaces and internal surfaces,

at least a portion of said internal surfaces being aluminum, aluminumalloy, titanium or titanium alloy; and

a coating comprising at least 12 wt % TiO₂ chemically adhered to atleast some of the aluminum, aluminum alloy, titanium or titanium alloyinternal surfaces thereby forming titanium dioxide containing coatedinternal surfaces;

wherein, portions of the engine that comprise titanium dioxide coatedinternal surfaces include surfaces that are contacted with intake air,fuel/air mix and/or exhaust gases during operation of said engine.

An aspect of the invention includes an engine further comprising anexhaust system comprised of an exhaust manifold and an exhaust pipewherein at least a portion of the exhaust system comprises said titaniumdioxide coated internal surfaces.

An aspect of the invention comprises an internal combustion engineincluding a variable volume combustion chamber defined by a pistonreciprocating within a cylinder between top and bottom center points anda cylinder head comprising an intake valve and an exhaust valve whereina portion of the internal combustion chamber comprises aluminum,aluminum alloy, titanium or titanium alloy surfaces, at least a portionof said surfaces having deposited thereon a coating comprising at least12 wt % TiO₂. In one embodiment, the engine is a four-stroke internalcombustion engine; in another embodiment, the engine is a two-strokeinternal combustion engine. In yet another embodiment, the combustionchamber is defined by a rotor and a rotary chamber.

In some embodiments, the coating is deposited electrolytically such thatan amorphous coating comprising at least 15 wt % TiO₂ is chemicallybonded to the aluminum, aluminum alloy, titanium or titanium alloysurfaces. In one embodiment, the titanium dioxide coating furthercomprises phosphorus, present in amounts of, in increasing order ofpreference, less than 10, 5, 2.5, 1 wt % and in increasing order ofpreference, at least 0.0001, 0.0005, 0.001, 0.005, 0.01, 0.05, 0.1, 0.5wt %. In one embodiment, the titanium dioxide coated surfaces exhibitthermal shock resistance to quenching in liquid nitrogen to −197° C.from a peak metal temperature of 550° C. (the alloy itself would melt iftaken above this temperature—the titanium dioxide coating is stable to900° C. in an oxidizing environment.

Another aspect of the invention includes a method to reduce NO_(x)emissions from an operating internal combustion engine, comprising:applying the aforementioned titanium dioxide coating to a portion ofsurfaces of the combustion chamber.

Except in the claims and the operating examples, or where otherwiseexpressly indicated, all numerical quantities in this descriptionindicating amounts of material or conditions of reaction and/or use areto be understood as modified by the word “about” in describing the scopeof the invention. Practice within the numerical limits stated isgenerally preferred, however. Also, throughout the description, unlessexpressly stated to the contrary: percent, “parts of”, and ratio valuesare by weight or mass; the description of a group or class of materialsas suitable or preferred for a given purpose in connection with theinvention implies that mixtures of any two or more of the members of thegroup or class are equally suitable or preferred; description ofconstituents in chemical terms refers to the constituents at the time ofaddition to any combination specified in the description or ofgeneration in situ within the composition by chemical reaction(s)between one or more newly added constituents and one or moreconstituents already present in the composition when the otherconstituents are added; specification of constituents in ionic formadditionally implies the presence of sufficient counter ions to produceelectrical neutrality for the composition as a whole and for anysubstance added to the composition; any counter ions thus implicitlyspecified preferably are selected from among other constituentsexplicitly specified in ionic form, to the extent possible; otherwise,such counter ions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word “mole”means “gram mole”, and the word itself and all of its grammaticalvariations may be used for any chemical species defined by all of thetypes and numbers of atoms present in it, irrespective of whether thespecies is ionic, neutral, unstable, hypothetical or in fact a stableneutral substance with well defined molecules; and the terms “solution”,“soluble”, “homogeneous”, and the like are to be understood as includingnot only true equilibrium solutions or homogeneity but also dispersions.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a drawing of portions of a four stroke internal combustionengine in accordance with the invention, including a partialcross-sectional view of the engine area occupied by the combustionchamber of the engine.

FIGS. 2 and 3 show transmission electron micrographs of the externalsurface of tested titania coatings deposited on aluminum substrates byplasma electrolytic deposition according the invention at two differentmagnifications.

FIG. 4 shows a micrograph of a fast ion bombardment cross-sectionthrough the aluminum substrate 400 and the titania coating 300, withpores 100, deposited on an aluminum substrate by plasma electrolyticdeposition according the invention with a top coating of platinum 200.

FIG. 5 shows a glow discharge optical emission spectroscopy (GDOES) of a13-14 micron thick titania coating on aluminum having a vanadium dopantpresent in the electrolyte and deposited in the titania coating.

FIG. 6 shows graphs of NOx emissions for coated cylinder heads at variedengine RPM and air/fuel ratios.

DETAILED DESCRIPTION OF THE INVENTION

An aspect of the invention comprises a method and apparatus for reducingat least one of HC, CO, and NO_(x) emissions from an operating internalcombustion engine including a combustion chamber, wherein a portion ofthe internal combustion chamber has aluminum or titanium containingsurfaces coated with adherent metal oxide, chemically bonded to thesurfaces, preferably containing titanium dioxide as described herein.

Suitable combustion chambers include rotors and rotor chambers of rotaryengines and variable volume combustion chambers, for example two orfour-stroke engine combustion chambers defined by a piston reciprocatingwithin a cylinder between top and bottom center points and a cylinderhead. The combustion chambers typically comprise an intake valve and anexhaust valve which may also be coated with titanium dioxide asdescribed herein. The internal combustion engine may utilize any fuelthat generates HC, CO, and/or NO_(x) exhaust emissions upon combustionin air, e.g. organic fuels including alcohol-based and hydrocarbonfuels, such as gasoline, gasoline/oil mixtures, kerosene or diesel, andthe like. The engine may use fuel injection, carburetor or other meansof supplying fuel, known in the art. Spark plugs, glow plugs or otherknown means for igniting the fuel/air mixture in the combustion chambermay be used. A portion of surfaces of each combustion chamber has asurface coating of titanium dioxide deposited thereon which functions toincrease decomposition rate of HC, CO, and/or NO_(x), and/or reduceformation rate of CO and/or NO_(x) reaction products of combustionreactions taking place in the combustion chamber.

The general operation and construction of an engine having surfacecoatings for purifying an exhaust gas according to the present inventionis that of a two or four stroke internal combustion engine or rotaryinternal combustion engine, which may be mounted on, for example, amotorized vehicle or other apparatus. Typically, such engines comprisemultiple combustion chambers made up of multiple cylinders and a pistoninserted in each cylinder, or at least one rotor chamber having at leastone rotor installed in the rotor chamber. Optionally, the cylinder orrotor chamber may additionally comprise a liner as is known in the art.If a liner is present, a surface of the liner may be coated according tothe invention instead of or in addition to a surface of the cylinder orrotor chamber.

An ignition source, such as a spark or glow plug, connected to anignition circuit is provided for each combustion chamber in a mannerknown in the art and when actuated, ignites fuel/air mixture in thecombustion chamber. In some engines, for example diesel engines, afterinitial start-up of the engine, the ignition source is compression ofthe fuel/air mixture. A fuel source, for example one or more fuelinjection valves that directly inject fuel into a combustion chamber, isprovided. In some embodiments, the direct fuel injection valve isreplaced with port injection, a carburetor, a throttle body or similardevice(s) that introduces a fuel or fuel/air mixture to the combustionchamber. The combustion chamber is in communication with a source ofair, such as for example one or more air-intake passages, via anair-intake port. Typically an air-intake passage supplies drawn air tothe combustion chamber of the engine. The section of the air-intakepassage on the downstream side may diverge into independent passages,each of which corresponds to individual cylinders, in communication withthe air-intake ports of the respective cylinders. An exhaust manifoldfor emitting exhaust gas from the combustion chamber communicates withthe combustion chamber through an exhaust gas port. The exhaust manifoldmay be diverged at the upstream end into passages, each of whichcorresponds to individual cylinders and in communication with thecombustion chamber of its respective cylinder via an exhaust gas valvethrough an exhaust gas port. In such an engine, the exhaust manifold maycontain an exhaust passage for each exhaust port in the cylinder head,and the manifold is fitted against the exhaust port area of the cylinderhead in a manner known in the art. The exhaust passages from each portin the manifold may join into a common single passage before they reachan manifold flange. An exhaust pipe is connected to the exhaust manifoldflange.

The exhaust manifold conducts the exhaust gases from the combustionchambers to the exhaust pipe. Many exhaust manifolds are made fromferrous metal. Exhaust systems or portions thereof to be coatedaccording to the invention may be aluminum, titanium, aluminum alloy,titanium alloy or may be another substrate having a layer of one of theaforesaid metals deposited thereon. The exhaust manifold, exhaust pipeand/or the tail pipe may be coated with a titanium dioxide coatingaccording to the invention. In one embodiment, at least a portion of aninterior surface of an exhaust manifold and/or an exhaust pipe is coatedwith a titanium dioxide coating as described herein.

Test data included herein demonstrates that operating characteristics ofan internal combustion engine change between an engine having aluminummetal combustion chamber surfaces, and a similar or the same enginehaving combustion chambers with at least a portion of the aluminumsurfaces covered with a titanium dioxide coating deposited as describedherein. Furthermore, it was observed experimentally that combustion ispositively affected by the presence of the titanium dioxide coatingchemically deposited as described herein during engine tests in severalways. First, the coating provides a protective layer when used onpistons which extended the life of a high performance engine piston setby at least two-fold by protecting the piston crown from heat damage.Second, there was a reduction in noxious emission gases of CO, NO, andunburned hydrocarbons (HC) for an engine that was operated with pistonscoated in titanium dioxide as described herein as compared to analuminum combustion chamber engine operated in like circumstances withuncoated pistons. Third, for combustion chamber surfaces which moveslidably in relation to each other, for example piston skirt portionsand cylinder walls, a coating of titanium dioxide deposited as describedherein provides improved adhesion of the coating and heat resistance ascompared to conventional coatings, including physically adhered pistoncoatings deposited by thermal spray and plasma assisted spraytechniques. Furthermore, when polished according to one aspect of theinvention, the coating provides reduced static and dynamic friction ascompared to the same coating in an unpolished state. The static anddynamic friction of a polished titanium dioxide surface was as good asor better than the diamond-like carbon (DLC) coatings recognized in theengine manufacturing industry as a performance benchmark for pistoncoatings.

The portion of each combustion chamber which may have a titanium dioxidecoating includes a surface portion of the piston, for example the skirtand/or crown; the surface of the walls of the cylinder; surfaces of theintake and exhaust valves; a surface portion of the cylinder headexposed to the combustion chamber, and various combinations thereof.Other non-combustion chamber portions of the engine that may be coatedinclude the air intake passages exhaust gas ports, and the exhaustsystem, meaning the exhaust manifold, exhaust pipe and tailpipe.

FIG. 1 shows aspects of one embodiment of the invention comprising aninternal combustion engine 1 having surface coatings for purifying anexhaust gas, which is shown for illustrative purposes only and not forthe purpose of limiting the invention. Purifying an exhaust gas will beunderstood in the context of this application to mean reducingconcentration of HC, CO and/or NO_(x) in exhaust gas emitted from anoperating internal combustion engine. For exemplary purposes only, theinternal combustion engine shown in FIG. 1 has a reciprocating pistonwhich moves up and down in a cylinder, but the description of theinvention can be readily understood to apply to a rotary engine as well.

In FIG. 1, the internal combustion engine 10 has an engine block 12comprising at least one cylinder 14 formed in the engine block, anengine head 20 comprising a cylinder head 21, and a reciprocating piston30 inserted in the cylinder 14. In FIG. 1, the walls 16 of the cylinder14, the cylinder head 21 and the moveable piston 30 define a variablevolume combustion chamber 40 in the engine. The reciprocating piston 30comprises a crown portion 31, having a surface area exposed to thecombustion chamber facing the cylinder head 21, and a body portion 32which conforms to the cylinder 14 in which it reciprocates. The bodyportion 32 comprises a skirt portion 34, generally understood in the artto be that part of the piston 30 located between the first ring groove36 and the bottom 38 of the piston 30. The skirt portion 34 comprises abearing area in contact with the cylinder wall 16. The skirt portion 34slides in relation to the cylinder wall 16 during reciprocating motionof the piston.

In this embodiment, an ignition plug 60 connected to an ignition circuit(not shown) is provided on the cylinder head 21 of the combustionchamber 40 in such a manner that the ignition electrode 62 faces thecombustion chamber 40 and when actuated ignites the air-fuel mixture inthe combustion chamber 40.

An injector (fuel injection valve) 70 that directly injects fuel to thecombustion chamber 40 is provided; in this embodiment it is located inthe engine head 20 on the rim of the combustion chamber 40. In someembodiments, the injector 70 is replaced with port injection, acarburetor, a throttle body or similar device(s) that introduces a fuelor fuel-air mixture to the combustion chamber. The various means ofintroducing fuel into a combustion chamber are known and not detailedherein.

The combustion chamber 40 is in communication with an air-intake passage22 via an air-intake port 24 that is opened and closed by an air-intakevalve 26. Likewise, the combustion chamber 40 is in communication withan exhaust passage 23 via an exhaust port 25 that is opened and closedby an exhaust valve 27. Flow of air through the air-intake port 24 iscontrolled by actuation of the air-intake valve 26 and flow of exhaustgases through the exhaust port 25 is controlled by actuation of theexhaust valve 27. The intake and exhaust valves have a combustionsurface portion, 28, 29 respectively, that is exposed to the combustionchamber 40. Desirably, the engine head 20 comprises one or more airintake ports 24 which supply air drawn through the air-intake passage 22to the combustion chamber 40 and one or more exhaust ports 25 throughwhich exhaust gases egress from the combustion chamber. The exhaustpassage 23 may merge with other such exhaust passages to form an exhaustmanifold (not shown) which leads to a common exhaust pipe exiting theengine compartment. In FIG. 1, an emission reducing coating 80 of metaloxide comprising titanium dioxide according to the invention is shown onportions of the surfaces defining the combustion chamber, namely thecylinder head 21 and the crown portion 31 of the piston 30.

Based on the description herein, those of skill in the art willunderstand application and use of the invention in alternativeembodiments of internal combustion engines such as two-stroke and rotaryengines. In one alternate embodiment, a rotary engine, for example aso-called Wankel engine, having at least one rotor and at least onerotor chamber may have portions of the engine coated according to theinvention. The rotary engine comprises intake and exhaust valves, intakeports, exhaust ports and an exhaust system as is known in the art. Eachof the rotor chambers accommodates at least one rotor. The rotor isformed by a generally-triangular block, each side of which has a bulgeat its central part when seen in the direction of the rotation axis. Therotor has, along its circumference, three generally-rectangular flanksurfaces between apexes. The rotor has apex seals on its respectiveapexes, which move along the surfaces of the rotor chamber as the rotormoves around the rotation axis. These apex seals together with innersurfaces of the rotor chamber and the flank surfaces of the rotor definethree working chambers inside the rotor chamber. The three workingchambers move in a circumferential direction while each working chambergoes through the intake, compression, combustion, and exhaustoperations, which respectively correspond to the intake stroke, thecompression stroke, the combustion stroke, and the exhaust stroke of thereciprocating engine. Combustion takes place serially in the workingchambers (combustion chambers) thereby turning the rotor. The rotor isgeared in a manner known in the art such that as the rotor makes onerotation, it turns a shaft in communication with the rotor and generatesrotational force, which is the engine output. Similar to thepiston/cylinder engines, portions of the rotary engine that may becoated with a titanium dioxide coating to reduce emissions and improveefficiency according to the invention include surfaces that define thecombustion chamber, namely a surface portion of the rotor, a surfaceportion of the rotor chamber; surfaces of the intake and exhaust valves;intake ports; exhaust ports; the exhaust system and various combinationsthereof. In one embodiment, surfaces which define the working chambersof the engine may be coated. In another embodiment, additional portionsof the engine that may be coated include air intake passages, exhaustgas ports, and the exhaust system, meaning the exhaust manifold, exhaustpipe and tailpipe.

There is no specific limitation on the aluminum, titanium, aluminumalloy or titanium alloy surface to be coated with the metal oxide,preferably titanium dioxide coating in accordance with the presentinvention. It is desirable for surfaces where the chemical deposition ofthe titanium dioxide coating is to be made electrolytically that thesurfaces comprise a metal that contains not less than, in increasingorder of preference, 30, 40, 50, 60, 70, 80, 90, 95, 100% by weighttitanium or aluminum.

The metal oxide coating desirably comprises at least 1, 5, 10, 15, 20,25, 30, 40, 50, 60, 70, 80, 90, 95, 99 wt % TiO₂. In some embodiments,the titanium dioxide coating is deposited electrolytically as describedherein and exhibits an amorphous morphology comprising surface pores 100which extend only partially into the coating layer 300. See FIG. 2-4.These pores are useful for, among other things, increasing surface areaof the coating and may assist in lubrication between the piston andcylinder walls in the combustion chamber. The surface area of thecoating relates to the amount of titanium or other active metal in thecoating that is available at the atmosphere/surface interface forcontacting the fuel and exhaust compositions in the engine to effectreduction in concentration of HC, CO and NO_(x). Desirably, the metaloxide coating provides a surface area to a substrate that is in a rangeof about 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150,160, 170, 180 times greater than the surface area of the substrate in anuncoated state. Greater surface area increases may be utilized providedthat other characteristics of the coating, e.g. adhesion, are notreduced such that benefits of the invention are not achieved. In oneembodiment, the titanium dioxide coating increased the surface area by146 times versus a bare flat aluminum panel as measured using the BETmethod.

In one embodiment, the titanium dioxide layer further comprisesphosphorus, present in amounts of, in increasing order of preference,less than 10, 5, 2.5, 1 wt % and in increasing order of preference, atleast 0.0001, 0.0005, 0.001, 0.005, 0.01, 0.05, 0.1, 0.5 wt %. Othersuitable additives may include effective amounts of other metals, andmetal oxides of the periodic table such as iron, cobalt, zirconium andother transition metals. Also traditional catalyst metals such asplatinum and the like may be included in the titanium dioxide coatingprovided that they do not interfere unduly with the objects of theinvention.

The titanium dioxide surface coating is sufficiently adherent to thealuminum and titanium surfaces such that less than 10, 9, 8, 7, 6, 5, 4,3, 2, 1, 0.5, 0.1, 0.01% of the coated surface area show blistering,delamination, or peeling of the surface coating after, in increasingorder of preference, 100, 150, 200, 250, 300, 350, 400, 450 500 hours ofcontinuous operation of the internal combustion engine at, in increasingorder of preference, 50, 60, 70, 80, 90 or 100% of maximum rpm undertemperature and lubrication conditions within engine manufacturer'sspecifications. Test data shows that endurance race car pistons after20,000 miles exhibited no soot build up or observable changes in thetitanium dioxide coating. In one embodiment, the titanium dioxidesurface coating shows less than 5, 4, 3, 2, 1, 0.5, 0.1, 0.01% of thecoated surface area show blistering, delamination, or peeling of thesurface coating after 150 hours of continuous operation of the internalcombustion engine at 100% of maximum rpm under temperature andlubrication conditions within engine manufacturer's specifications.

The titanium dioxide coating is insoluble in engine coolant andlubricants and generally has an amorphous morphology. Desirably thetitanium dioxide coating is resistant to thermal shock and thermalcycling such that no crazing or coating loss takes place when the coatedsurfaces are subjected to temperature cycling between −197° C. and 550°C. for at least in increasing order of preference of 1, 2, 3, 4, 5cycles. Desirably the titanium dioxide coated surfaces exhibit thermalshock resistance to quenching in liquid nitrogen to −197° C. from a peakmetal temperature of 550° C. Temperature resistance was tested onaluminum pistons and found to be greater than 600° C., the titaniacoating was still adherent to the piston surface despite heatdeformation of the piston.

In another test, resistance against thermal shocks was tested asfollows, a substrate coated with titania according to the invention wasmaintained at 600° C. for 84 h, followed by a water quench at 5° C.,thereafter the substrate was cross-hatched through the coating to thesubstrate and subjected to reverse impact testing. A coated controlpanel was also subjected to reverse impact testing. The results showedno loss of adhesion of the coating, showing that the Plasma ElectrolyticDeposition of a titania coating on an aluminum substrate resulted inchemically adherent coating with flexibility and adherence that meetsthe ball reverse impact test both before and after thermal shock. Thisis a significant improvement in adhesion as compared to plasma-depositedand other physically adhered coatings.

Generally, the titanium dioxide coating is deposited in a uniform layerhaving a thickness of between 1 and 20 microns. Lower thicknesses may beutilized for economy, provided that the coating is not so thin as tolose emission reduction benefits of the invention. Thicknesses of thecoatings are at least in increasing order of preference 1, 2, 3, 4, 5,6, 7, 8 or 9 microns and not more than in increasing order of preference20, 19, 18, 17, 16, 15, 14, 13, 12, 11, or 10 microns.

The titanium dioxide coating may optionally be polished to reducefriction between a first coated surface and a second surface that iscoated or un-coated which may contact the first coated surface. In thisembodiment, the surfaces to be coated are not limited to metal surfacesthat contact intake air, fuel/air mixtures and/or exhaust, but mayinclude internal or external wear surfaces. For this embodiment, thetitanium dioxide coating is desirably deposited electrolytically suchthat the coating is chemically bonded to the metal surface. Suitablesurfaces which may benefit from the coating are wear or contact surfacesof, for example, an engine, including plain bearings, rocker arms, camshafts, and other bearing surfaces as well as piston skirts, cylindersor cylinder liners whose design and function are known in the art.Contact points between the two surfaces may be intermittent orcontinuous. The combination of the strongly adherent feature of theelectrolytic coating and the polished surface of the coating provides along lasting, low friction coating.

Polishing may remove from at least, in increasing order of preference,1, 0.1, 0.01, or 0.001 wt % up to at most, in increasing order ofpreference, 90, 80, 70, 60, 50, 40, 30, 20, 10, 5, 2.5 wt % of thetitanium dioxide coating. In one embodiment, approximately 5-15 wt % ofthe coating is removed by polishing. In one embodiment, a polishedcoated surface has an Ra of 0.1 to 0.75 microns, desirably an Ra of 0.2to 0.5 microns, where Ra is the average surface roughness calculatedusing measurements taken with standard contact or non-contactprofilimetry devices.

In a preferred embodiment of the invention, the titanium dioxide coatingis deposited electrolytically. The electrolyte solution used compriseswater, a water-soluble and/or water-dispersible phosphorus oxy acid orsalt, for instance an acid or salt containing phosphate anion; andH₂TiF₆; H₂ZrF₆ is an optional ingredient. Preferably, the pH of theelectrolyte solution is neutral to acid (more preferably, 6.5 to 2). Thecombination of a phosphorus-containing acid and/or salt and the complexfluoride in the electrolyte solution produced a different type ofelectrolytically deposited coating. The oxide coatings depositedcomprised predominantly oxides of metals from anions present in theelectrolyte solution prior to any dissolution of the metals in the metalsurface on which the coating was being deposited. That is, this processresults in coatings that result predominantly from deposition ofsubstances that are not drawn from the surface being coated, resultingin less change to the substrate of the article being coated, see FIG. 5.This feature is beneficial where the size and shape of enginecomponents, which are typically designed within narrow tolerances, arenot changed by the above-described coating process and the coatingdeposits uniformly and at a controlled thickness. In this embodiment, itis desirable that the electrolyte solution comprise the at least onecomplex fluoride, e.g. H₂TiF₆, and optionally H₂ZrF₆, in an amount of atleast, in increasing order of preference 0.2, 0.4, 0.6, 0.8. 1.0, 1.2,1.3, 1.4, 1.5, 2.0, 2.5, 3.0, 3.5 wt. % and not more than, in increasingorder of preference 10, 9.5, 9.0, 8.5, 8.0, 7.5, 7.0, 6.5, 6.0, 5.5,5.0, 4.5. 4.0 wt. %. The at least one complex fluoride may be suppliedfrom any suitable source. The phosphorus oxysalt may be supplied fromany suitable source such as, for example, ortho-phosphoric acid,pyro-phosphoric acid, tri-phosphoric acid, meta-phosphoric acid,polyphosphoric acid and other combined forms of phosphoric acid, as wellas phosphorous acids and hypo-phosphorous acids, and may be present inthe electrolyte solution in partially or fully neutralized form (e.g.,as a salt, wherein the counter ion(s) are alkali metal cations, ammoniumor other such species that render the phosphorus oxysalt water-soluble).Organophosphates such as phosphonates and the like may also be used (forexample, various phosphonates are available from Rhodia Inc. and SolutiaInc.) provided that the organic component does not interfere with theelectrolytic deposition. Preferred is the use of a phosphorus oxysalt inacid form. The phosphorus concentration in the electrolyte solution isat least 0.01 M. It is preferred that the concentration of phosphorus inthe electrolyte solution be at least, in increasing order of preference,0.01M, 0.015, 0.02, 0.03, 0.04, 0.05, 0.07, 0.09, 0.10, 0.12, 0.14,0.16. In embodiments where the pH of the electrolyte solution is acidic(pH<7), the phosphorus concentration can be 0.2 M, 0.3 M or more andpreferably, at least for economy is not more than 1.0, 0.9, 0.8, 0.7,0.6 M. A preferred electrolyte solution for use in forming a protectivetitanium dioxide coating according to this embodiment on an aluminum ortitanium containing surface may be prepared using the followingcomponents:

H₂TiF₆ 0.05 to 10 wt. % H₃PO₄ 0.1 to 0.6 wt. % Water Balance to 100%In carrying out the electrolytic coating of engine components, thecoating bath is maintained at a temperature between 0° C. and 90° C. ApH adjuster may be present in the electrolyte solution; suitable pHadjusters include, by way of non-limiting example, ammonia, amine orother base. The amount of pH adjuster is limited to the amount requiredto achieve a pH of 1-6.5, preferably 2-6, most preferably 3-5.

The electrolytic coating process comprises immersing portions of theengine or articles having wear surfaces having aluminum and/or titaniumcontaining surfaces that are to be coated with the titanium dioxidecoating in the electrolytic coating solution, which is preferablycontained within a bath, tank or other such container. The aluminumand/or titanium containing surfaces are connected as the anode and asecond metal article or the tank itself is connected as the cathode.Electric current is passed between the cathode and anode through theelectrolyte for a selected period of time sufficient to cause depositionof an adherent, amorphous titanium dioxide coating on the aluminumand/or titanium containing surfaces. The coated article is removed fromthe coating bath and rinsed. Other treatments may be performedthereafter to these surfaces prior to assembly, including polishingand/or painting. In depositing the titanium dioxide coatingelectrolytically, direct current (DC) is preferably used, and it may bepulsed or non-pulsed direct current. Alternating current (AC) may alsobe used, with voltages desirably between 200 and 600 volts (under someconditions, however, the rate of coating formation may be lower usingAC). The frequency of the wave may range from 10 to 10,000 Hertz; higherfrequencies may be used. In one embodiment, direct current (DC) pulsedor non-pulsed is used at an average of 200 to 1000 volts.

In one embodiment, the current is pulsed or pulsing direct currentdesirably used in the range of at least, in increasing order ofpreference 200, 250, 300, 350, 400 volts and at least for the sake ofeconomy, not more than in increasing order of preference 1000, 900, 800,700, 650, 600, 550 volts. The “off” time between each consecutivevoltage pulse preferably lasts between 10% as long as the voltage pulseand 1000% as long as the voltage pulse. During the “off” period, thevoltage need not be dropped to zero (i.e., the voltage may be cycledbetween a relatively low baseline voltage and a relatively high ceilingvoltage). The baseline voltage thus may be adjusted to a voltage that isfrom 0% to 99.9% of the peak applied ceiling voltage. The current can bepulsed with either electronic or mechanical switches activated by afrequency generator. When using pulsed current, the average voltage ispreferably not more than 500 volts, more preferably, not more than 450volts, or, most preferably, not more than 400 volts, depending on thecomposition of the electrolyte solution selected. The peak voltage, whenpulsed current is being used, is preferably not more than 1000, 900,800, 700, 600, preferably 500, most preferably 400 volts. In oneembodiment, the peak voltage for pulsed current is not more than, inincreasing order of preference 600, 575, 550, 525, 500 volts andindependently not less than 300, 310, 320, 330, 340, 350, 360, 370, 380,390, 400 volts. In one alternating current embodiment, the voltage is,in increasing order of preference 600, 575, 550, 525, 500 volts andindependently not less than 300, 310, 320, 330, 340, 350, 360, 370, 380,390, 400 volts. In the presence of phosphorus containing components,non-pulsed direct current, also known as straight direct current, may beused at voltages from 200 to 600 volts. The non-pulsed direct currentdesirably has a voltage of, in increasing order of preference 600, 575,550, 525, 500 volts and independently not less than 300, 310, 320, 330,340, 350, 360, 370, 380, 390, 400 volts. The average amperage per squarefoot is at least in increasing order of preference 10, 20, 30, 40, 50,60, 70, 80, 90, 100, 105, 110, 115 Amps/ft², and not more than at leastfor economic considerations in increasing order of preference 400, 350,300, 275, 250, 225, 200, 180, 170, 160, 150, 140, 130, 125 Amps/ft².More complex waveforms may also be employed, such as, for example, a DCsignal having an AC component. The higher the concentration of theelectrolyte in the electrolyte solution, the lower the voltage can bewhile still depositing satisfactory coatings.

Titanium dioxide coatings, as well as other metal oxide coatings,deposited electrolytically by the above-described method are chemicallybonded to the metal surface and have increased surface area as comparedto the uncoated aluminum panel. Desirably, the metal oxide coating has asurface area that is in a range of about 20, 30, 40, 50, 60, 70, 80, 90,100, 110, 120, 130, 140, 150, 160, 170, 180 times greater than anuncoated flat aluminum panel surface. Greater surface area increases maybe utilized provided that other characteristics of the coating, e.g.adhesion, are not reduced such that benefits of the invention are notachieved. The coating has insolubility in lubricant and coolant,adherence that is resistant to thermal cycling and thermal shock asdescribed above, and wear resistance suitable for use in the combustionchamber and/or exhaust system with blistering, delamination and peelingresistance as described herein.

Other methods of depositing titanium dioxide containing coatings may beacceptable provided that increased decomposition rate and/or reducedformation rate of at least one of HC, CO, and NO_(x) emissions fromcombustion taking place in the combustion chamber as described above isachieved and the coating has sufficient durability to be used in thecombustion chamber and/or the exhaust system.

The invention may be practiced by coating all surfaces of an internalcombustion engine that contact intake air, fuel/air mixture and/orexhaust gas during engine operation with the metal oxide containingtitanium dioxide or only a portion of these surfaces. At least foreconomy's sake, it may be preferable to determine a target reduction inconcentration of HC, CO or NO_(x) in exhaust gas discharged, and coat asufficient number of surfaces or surface area to achieve the reduction.As shown by the test data below, the operating parameters of the engineaffect the emissions produced. It is desirable to determine the state ofengine operating parameter(s) resulting in an emission value so thatmeaningful comparisons of emissions with and without the invention canbe made to allow deposition of the coating on sufficient surfaces toeffect the target reduction in concentration of at least one of HC, COand NO_(x) in exhaust gas discharged. Engine operating parametersinclude, by way of non-limiting example, engine speed, torque, load,exhaust gas recirculation (EGR) and indicated mean effective pressure(IMEP). According to one method of the invention, the method to reduceemissions from an operating internal combustion engine, comprises thesteps of determining a state of an engine operating parametercorresponding to an emission value of at least one of HC, CO and NO_(x)emitted from a combustion chamber of an operating internal combustionengine; determining a target reduction in concentration of at least oneof HC, CO and NO_(x) in exhaust gas discharged from the operatinginternal combustion engine corresponding to the state of the engineoperating parameter corresponding to the emission value of at least oneof HC, CO and NO emitted from the combustion chamber of the operatinginternal combustion engine, wherein the concentration of the at leastone of HC, CO and NO_(x) is measured at a selected location in a path ofthe exhaust gas that is downstream from the combustion chamber; anddepositing a titanium dioxide containing coating on a portion ofsurfaces of

a. the combustion chamber;b. an air-intake passage in communication with the combustion chamber;c. an exhaust passage in communication with the combustion chamber;d. intake and/or exhaust valves; and/ore. an exhaust manifold in communication with the exhaust passage;to effect said target reduction.

In one embodiment, piston skirts and/or cylinder walls, or the rotarychambers, coated with a titanium dioxide coating as described herein aresubsequently polished to reduce surface roughness. The method ofpolishing the titanium dioxide surface comprises physically removing, atleast in increasing order of preference 1, 2, 3, 4 or 5 wt % and notmore than in increasing order of preference 90, 80, 70, 60, 50, 40, 30,20, 10 wt % of the coating. Any known polishing means are suitable. Onemethod for polishing comprises use of abrasive having a grit of lessthan in increasing order of preference 45, 40, 35, 30, 25, 20, 15, 10,5, 4, 3, 2, 1 micron. The composition of the grit can be those known inthe art, for example, diamond, cerium oxide, zirconium oxide, ferricoxide, silicon carbide and the like. In one embodiment, a polishedcoated surface is polished such that it has an Ra of 0.01, 0.05, 0.1,0.15, 0.2, 0.25, 0.3 microns to not more than 0.4, 0.45, 0.5, 0.6, 0.7,0.8, 1.0 microns.

In an alternative embodiment, the titanium dioxide coated internalsurfaces of the engine may be subsequently coated with a secondarycoating to provide additional desirable properties to coated internalsurfaces of the engine. A non-limiting example includes dry filmlubricants, such as graphite, molybdenum disulfide, polymer coatingscontaining graphite and/or molybdenum disulfide, fluoropolymers,silicones or waxes and titanium dioxide coatings deposited viaPlasma-Assisted Layer Deposition (PALD) or thermal spray.

It has been surprisingly discovered that doping the titania coating withcertain metals can improve NOx emissions even further. Doping, that isadding other elements or compounds to the titania coating, can beaccomplished by adding soluble or finely dispersed solids to theelectrolyte which may be deposited as or provide components incorporatedas dopants in the titania coating or by adding a dopant after coating.Generally, any metal or metalloid element that provides a reduction inHC, CO or NOx in exhaust gases can be used provided that the compound orstructure of a resulting dopant, containing the metal or metalloidelement, that is in or on the titania is stable to the use environmente.g. temperatures and chemistries, such that it remains active. Examplesof use environments include one or more of a combustion chamber, exhaustpassages, exhaust manifold and downstream exhaust system components,upstream of any catalytic converter present, of an internal combustionengine.

Incorporating dopant into the titania coating during PED can beaccomplished by doping the electrolyte with a liquid or a solid dopantgenerating composition. The liquid or solid dopant generatingcomposition can be soluble or small particles of insoluble additives orsubstances that are easily decomposed to release metal or metalloids.The liquid or solid dopant generating composition is added to theelectrolyte in an amount such that during PED, the dopant is depositedin or on the titania coating. Suitable examples of soluble dopantgenerating compositions include metals and metalloids of the PeriodicTable and salts and oxides thereof, in particular transition metalsincluding actinide and lanthanide series, for example cerium, silver,gold, platinum, palladium, rhodium, cobalt and/or vanadium. Smallparticles of insoluble additives such as nanoparticulate metals,metalloids and compounds thereof may be incorporated into the titaniacoating or into the pores thereof from the electrolyte. Suitableparticulate compounds can be for example, nitrides, oxides, carbides,sulfides and the like. Particle diameters typically range from aboutless than in increasing order of preference 100, 90, 80, 70, 60, 50, 40nanometers and as small as in increasing order of preference, 35, 30,25, 20, 15, 10, 5, 4, 3, 2, or 1 nanometers.

Post-coating doping of the titania coating can be accomplished bycontacting with a liquid or a solid dopant generating composition.

Liquid post-coating doping can be through deposition of a liquidadditive that is dried in place, a reactive liquid that generates thedopant in situ (e.g. an alkoxy titanate can be used to generate asecondary titania have different properties or crystal structure inaddition to the PED titania), or a liquid that is heat or otherwisetreated to generate the dopant. For example, a liquid containing a metalnitrate may be applied and subsequently heated. The metal from the metalnitrate is effectively deposited into the titania matrix and the nitrateis driven off as oxides of nitrogen. Similar processes can be run usingmetal alkoxides and metal ligand systems.

Solid post-coating doping can be through deposition of a solid additiveinto the porous titania matrix or by generation of the dopant in situ.Suitable examples of solid post-coating doping include PVD, for examplesputtering, CVD, for example radio frequency CVD, gas plasma CVD,shotblasting, burnishing, wiping. Particle diameters typically rangefrom about less than in increasing order of preference 100, 90, 80, 70,60, 50, 40 nanometers and as small as in increasing order of preference,35, 30, 25, 20, 15, 10, 5, 4, 3, 2, or 1 nanometers.

Suitable examples of thus deposited dopants include metals andmetalloids of the Periodic Table and oxides thereof. Transition metalsincluding actinide and lanthanide series metals, in particular membersof Groups 2-15, or Groups 3-12.

Substances that are easily oxidized include metal nitrates that willcontribute metal oxides to the titania. Suitable examples of solublesubstances include nitrates, acetates, alkoxy or other metal ligandsystems capable of release of a metal or metalloid into the titaniamatrix.

Applicants tested a stock aluminum cylinder head, a titania coatedcylinder head and several cylinder heads wherein the titania coatingfurther comprised one of the following metals: cobalt, platinum andvanadium on a four-stroke internal combustion engine, see Example 10below. The results showed that doping the high surface area titaniacoating can further reduce NOx emissions as compared to either a stockaluminum cylinder head or a titania coated cylinder head, at lean,stoichiometric and rich air/fuel ratios, see FIG. 6 a-6 d.

EXAMPLES Example 1 Coating Internal Surfaces

A commercially available V8 cast aluminum air intake component,identical to the cast aluminum air intake component of ComparativeExample 1, was alkaline cleaned by immersion for 5 minutes in Ridoline298, an alkaline cleaner commercially available from Henkel Corporation.The part was rinsed with water and was immersed in an aqueouselectrolyte solution prepared using 20.0 g/L H₂TiF₆ (60%) and 4.0 g/LH₃PO₄. The pH was adjusted to 2.2 using aqueous ammonia. The article wassubjected to electrolytic treatment for 3 minutes in the electrolytesolution using pulsed direct current having a peak ceiling voltage of450 volts (approximate average voltage=290 volts) at 90° F. The “on”time was 25 milliseconds, the “off” time was 9 milliseconds (with the“off” or baseline voltage being 0% of the peak ceiling voltage). Theaverage current density was 80 amps/ft. No auxiliary electrodes wererequired; the counter electrodes were placed more than 13 inches fromthe outside of the part. The part was removed from the bath, rinsed withwater and inspected. A uniform coating, 10 microns in thickness, wasformed on the surface of the aluminum intake component. The coating wasdeposited over the entire air intake component, including the inside ofthe cooling tunnels and other areas of the casting. The coating wasfound to be predominantly titanium dioxide. Traces of phosphorus, lessthan 10% were also seen in the coating.

Example 2 Gasoline Engine Air Intake Coating

A production small block Ford V-8 engine with standard cast aluminum airintake component was tested as a comparative uncoated example(Comparative Example 1). The titanium dioxide coated cast aluminumintake component of Example 1 was installed on the V-8 engine in placeof the stock intake and the tests were run again (Example 2). Resultsare shown below indicating an increase in horsepower and torque for thecoated air intake component.

TABLE 1 Horsepower Max. Torque Max. Substrate RPM 5700 RPM 4400 Example2, coated 337.35 340.92 Comparative Example 1, uncoated 326. 330.Improvement %: 3.3% 3.3%The increase in horsepower and torque showed improved power from similaroperating conditions tending to show improved utilization of fuel by theengine when the coated intake was used.

Example 3 Thermal Shock

Two commercially available, after-market aluminum pistons for anautomotive engine were obtained from the same supplier for comparativetesting. One piston was bare aluminum and the second piston wassubstantially the same, but had an existing skirt coating based uponorganic polymers mixed with solid film lubricants, see Example 3 andComparative Example 2, respectively.

Example 3

The bare aluminum piston for an automotive engine was treated accordingto Example 1. The entire piston, including the wrist pin bore, skirt andtop of the piston were uniformly coated with a layer of titaniumdioxide. The piston did not require selective coating or any oventreatment, which is typically required to coat pistons having aconventional separate skirt coating. The coated piston was heated to550° C. for 16 hours and then immediately placed in 5° C. water. Thecoating on the piston and the piston body were unaffected, i.e.unchanged, by the high temperature treatment and were also unaffected bythe thermal shock test, i.e. no warpage, cracking, blisteringdelamination or crazing was observed.

Comparative Example 2

The aluminum piston having an existing skirt coating based upon organicpolymers mixed with solid film lubricants was heated to 450° C. After 4hours at 450° C., the conventional skirt coating was completely removedfrom the piston surface, leaving the bare aluminum substrate exposed.

Example 4 Adhesion

Adhesion of metal oxide coating electrolytically deposited was conductedwith and without secondary coatings applied.

Example 4-1 Flat Panels Having Electrolytic Coating with SecondaryCoating

For Examples 4A-D, clean desmutted 6063 aluminum alloy panels werecoated, using an electrolyte solution prepared using H₂TiF₆ (60%) 20.0g/L and H₃PO₄ (75%) 4.0 g/L. The panels were subjected to electrolyticcoating treatment at pH 2 for 3 minutes in the electrolyte solutionusing pulsed direct current having a peak ceiling voltage of 450 volts(approximate average voltage=130 volts) at 90° F. The “on” time was 10milliseconds, the “off” time was 30 milliseconds (with the “off” orbaseline voltage being 0% of the peak ceiling voltage). A uniformcoating, 7.6 microns in thickness, was formed on the surface of thealuminum-containing panels of Examples 4A-D. For Comparative ExamplesA-D, 6063 aluminum alloy panels were shot-blasted according to standardindustry practice.

Each panel of Examples 4A-D and Comparative Examples A-D was thenthermal spray coated using high velocity oxy-fuel (HVOF) with a thermalspray coating as disclosed in Table 2. Each panel was thereaftersubjected to adhesion testing according to ASTM D3359 wherein thecoatings were crosshatched and subjected to adhesion tests whereincommercially available 898 tape was firmly adhered to each film and thenpulled off at a 90° angle to the surface. The results below show thatthe electrolytically deposited coating was not removed at all and thatsecondary layers of thermal spray, which are only physically adhered,had improved adhesion to the surfaces coated with the titanium dioxide.

TABLE 2 Thermal Spray Test Results from Example Electrodeposited LayerApplied Coating ASTM D 3359 Comparative Shot blasted, Titania ThermalSpray - 0B 100% loss of A no electrodeposited layer 99 wt % TiO₂ thermalspray coating 4A Electrodeposited TiO₂ Layer Titania Thermal Spray - 5BPerfect Present 99 wt % TiO₂ 0% loss Comparative Shot blasted, AluminaThermal Spray - 0B B no electrodeposited layer 98.5 wt % Al₂O₃; 1.0 wt %SiO₂ 70% loss 4B Electrodeposited TiO₂ Layer Alumina Thermal Spray - 4BPresent 98.5 wt % Al₂O₃; 1.0 wt % SiO₂ Less than 1% loss ComparativeShot blasted, Zirconia Thermal Spray - 1B C no electrodeposited layer 80wt % ZrO₂; 20 wt % Y₂O₃ 50% loss 4C Electrodeposited TiO₂ Layer ZirconiaThermal Spray - 4B Present 80 wt % ZrO₂; 20 wt % Y₂O₃ Less than 1% lossComparative Shot blasted, 79 wt % Fe, 18 wt % Mo, 0B D noelectrodeposited layer 7.0 wt % C 70% loss 4D Electrodeposited TiO₂Layer 79 wt % Fe, 18 wt % Mo, 5B Perfect Present 7.0 wt % C 0% loss

Example 4-2 Reverse Impact Adhesion Testing of Flat Panels Having BareElectrolytically Deposited TiO₂ Coating

An aluminum alloy panel was first electrolytically coated with atitanium dioxide coating having film thickness of 8-12 microns. The testpanel was then crosshatched per ASTM D3359 method B, down to theunderlying aluminum surface. Reverse impact testing was performed perASTM D2794 by directly impacting the back-side of the crosshatched areaof the coated panel. Testing was performed at 110 in lb with a 4 lbweight. Then adhesion was checked using ASTM standard widesemi-transparent pressure sensitive tape. The subsequent tape pullrevealed no loss of adhesion of the electrolytically deposited coatingdespite fracture of the panel at the cross-hatched area due to theimpact testing.

Example 4-3 Engine Component, Piston, Having Electrolytic TiO₂ Coatingwith Secondary Coating

A commercially available, bare aluminum piston was coated as inExample 1. Thereafter, an aqueous mixture of 10% NeoRez® R9679 and 10%Aquagraph 6201 was applied to the coated piston to form a dry film sealto act as a lubricant to reduce the coefficient of friction and improvewear resistance in the event of a low or no oil event in the internalcombustion engine. NeoRez® R9679 is an aliphatic aqueous colloidaldispersion of a urethane polymer containing 37% by weight solids(specific gravity of the solids is 1.16 and acid number of resin solidsis 17.0), and is commercially available from Zeneca Resins, Inc.,Wilmington, Mass. Aquagraph 6201 is a commercially available aqueousgraphite slurry. The sealant was dried on the coated piston at 190° C.for 5 minutes. The resin bonded dry film lubricant showed good adhesionto the coated piston; there was no flaking, peeling or blistering of thelubricant.

Example 5 Diesel Engine Testing

A diesel fueled internal combustion engine having a variable volumecombustion chamber defined by a piston, reciprocating within a cylinderbetween top and bottom points, and a cylinder head comprising twoair-intake valves and two exhaust gas valves was selected for testing.The piston and head were aluminum alloy. The engine was operated withoutany titanium dioxide coating in the combustion chamber at various engineoperating parameters including test speeds (rpm), IMEP and EGR withvaried loading as described below, and noise level and emissions weremeasured (Control). Thereafter, the piston and the cylinder head of theengine were removed and the piston crown and cylinder head were treatedaccording to Example 1 (Coated). The engine was reassembled and testedunder the same operating conditions as the uncoated engine to allow forcomparison of data. The results of the testing of coated and uncoatedengines are shown in the tables below.

TABLE 3 2000 rpm Uncoated Coated Engine sound level (dB) Noise 88 87Indicated Efficiency (%) 41.5 41.9 CO (g/kWh) 5.8 3.8 HC (g/kWh) 0.750.65 NO_(x) Emissions (ppm) 152 148

Another engine operating parameter, percent of Emission Gas Recycling(EGR %) was varied across 40%, 43% and 46% at engine speed of 1500 rpmand 6.8 bar IMEP and carbon monoxide emissions (CO), hydrocarbonemissions (HC) and oxides of nitrogen (NO_(x)) emissions were measured,see the table below.

TABLE 4 CO HC NO_(x) Emissions NO_(x) Emission (g/kWh) (g/kWh) (g/kWh)Reduction EGR (%) Uncoated Coated Uncoated Coated Uncoated Coated Coated40 2.85 2.7 0.64 0.55 0.65 0.61 6% 43 3.3 3.3 0.66 0.58 0.49 0.43 8.8% 46 4.2 3.9 0.7 0.6 0.30 0.29 2%

The above table shows significant reductions in HC and NO_(x) emissions.

EGR (%) was varied across 38% and 41% at engine speed of 1500 rpm and4.3 bar IMEP and additional measurements of CO, HC and NO_(x) emissionswere taken. At 41% EGR the CO and HC emissions were similar, and withinexperimental error of each other for coated and uncoated. At 38% EGR,the samples showed less CO and HC emissions for the coated sample.Surprising reductions in NO_(x) emissions at both EGR values were notedwhen the engine with coating was compared to the engine without thecoating, see the table below.

TABLE 5 NO_(x) Emissions NO_(x) Emission (g/kWh) Reduction EGR (%)Uncoated Coated Coated 38 0.95 0.65 31% 41 0.69 0.40 42%

Test results also showed that for engine speed of 1500 rpm and 4.3 barIMEP, the engine having the titanium dioxide coated parts had higherpercentage efficiency where both engines were tested under comparableconditions. Specifically, the engines were tested at substantially thesame values over a range of engine operating parameters includingrelative air/fuel ratio, mass flow of humid air and EGR % s; formeasured amounts of NO_(x) emissions ranging from 0.1 g/kWh to 2.0g/kWh, the coated engine parts delivered greater indicated efficiencypercents at NO_(x) emissions of 0.3 g/kWh and above. These efficienciesamounted to greater than 1% improvement in engine efficiency.

Example 6 Gasoline Engine Testing

An LE5 four cylinder automotive gasoline (unleaded) engine was used fortesting using a dynamometer calibration from a corresponding productionvehicle. The engine was a 2.4 L port-injected engine with variable valvetiming having cast aluminum block. Two sets of parts were tested, eachset consisting of four pistons and a head made of aluminum. One set ofparts was coated according to Example 1 (coated). A second set of partswas an essentially unmodified production engine set (control) andprovides a Comparative Example. The valve seats in the head of thecoated part set were modified from stock design to accommodate thethickness of the coating. The same modification was made to the valveseats of the uncoated head. Both heads had similar flow characteristics.The same engine was used for testing both sets of parts to reducevariations from engine to engine. The engine was connected to adynamometer equipped with a controller and exhaust missions weremeasured using an emission measurement apparatus commercially availablefrom Horiba Instruments Inc., using the following procedure: Engineemissions from the fully warmed up engine were evaluated. Sevendifferent speed and load points were evaluated which are representativeof the operation of the engine over a FUDS cycle which is used toevaluate emissions for urban driving in the United States. Thedynamometer was operated at the target speed in speed control mode. Theengine throttle was controlled to maintain constant torque. The enginewas allowed to reach a stable condition before measurements were taken.The engine was swept through a number of different equivalence ratioswhile emissions were recorded for a sixty second period at 100 Hz.

The results below compare the data from running the engine with theuncoated “control” parts using commercially available oil without Moly(Comparative Example) to data from running the engine with the “coated”parts using Moly oil. Moly oil was commercially available motor oilcontaining oil soluble molybdenum compositions. The detailed data wasanalyzed to determine the emissions concentrations at an equivalenceratio of 1.0 which is the target EQR for a stoichiometric engine.Summary results for each point at an EQR of 1.0 are provided below.

TABLE 6 Total Exhaust Hydrocarbon Concentration (ppm) for Coated Parts(Example) and Control (Comparative Example) Parts 1000 1600 1600 16002200 2200 2200 rpm, rpm, rpm, rpm, rpm, rpm, rpm, 30 kPa 20 kPa 60 KpaWOT 20 Kpa 60 kPa WOT control 3000 2200 1800 1050 1800 1600 900 coated1500 1900 1800 1050 1100 1100 800

TABLE 7 Carbon Monoxide Concentration (%) for Coated Parts (Example) andControl (Comparative Example) Parts 1000 1600 1600 1600 2200 2200 2200rpm, rpm, rpm, rpm, rpm, rpm, rpm, 30 kPa 20 kPa 60 Kpa WOT 20 Kpa 60kPa WOT control 2.2 0.8 0.5 1.4 0.75 0.6 0.5 coated 1.4 0.6 0.6 0.5 0.750.6 0.4

TABLE 8 NO_(x) Concentration (ppm) for Coated Parts (Example) andControl (Comparative Example) Parts 1000 1600 1600 1600 2200 2200 2200rpm, rpm, rpm, rpm, rpm, rpm, rpm, 30 kPa 20 kPa 60 Kpa WOT 20 Kpa 60kPa WOT control 1100 1400 3200 2050 1600 3000 2400 coated 1000 1250 26001300 800 1800 1600

The results in the foregoing three tables demonstrate the coated engineproducing reduced amounts of HC, CO and NO_(x) in exhaust emissions ascompared to the engine in the uncoated state.

Example 7 Surface Area Testing

For this experiment, an aluminum-sample 1 cm×2 cm (thickness 0.8 mm) wascoated on both sides according to the procedure of Example 1, resultingin an approximately 10 μm thick coating comprising predominantlytitanium dioxide with traces of phosphorus, less than 10%.

The dry, coated sample was weighed. Liquid nitrogen was adsorbed on thesurface of the coated sample. The sample was then heated and re-weighed.The weight loss (caused by desorbing nitrogen) was determined. From theamount of desorbing nitrogen, the specific surface area that was coveredby nitrogen was calculated by the BET method. This value was compared tothe geometrical surface area of the sample determined by the sampledimensions. The coating increased the surface area by 146× (times) equalto 14,600% versus a bare flat panel.

Example 8 Gasoline Engine Testing

Emissions of coated parts from Example 6 were retested and compared tothose of stock parts using the test procedure of Example 6, modified inthat the engine controller was used to operate the engine in a normalclosed-loop control mode. The emission results are shown in Tables onthe next page.

On average, the coated part set showed a 3% reduction in the carbonmonoxide emissions, 13% reduction in the hydrocarbon emissions, and a32% reduction in the NO_(x) emissions compared to the stock part set.

Example 8 Tables

TABLE 9 Total Hydrocarbon (ppm) Results for Coated Parts and Stock Parts1840 1840 1698 1698 2125 2125 1698 2268 1413 1413 1555 1983 1555 18401983 1555 rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm,rpm, rpm, rpm, rpm, 11 115 70 112 22 75 100 95 70 113 38 110 114 72 6651 ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lbft-lb ft-lb ft-lb ft-lb ft-lb Stock 2269 1748 1347 1414 3131 1194 1075984 1325 805 1690 1357 1222 1642 1499 1417 Coated 2700 1505 1153 11511710 1028 1042 911 1224 881 1409 1080 1155 1162 1104 1201

TABLE 10 Carbon Monoxide (%) Results for Coated Parts and Stock Parts1840 1840 1698 1698 2125 2125 1698 2268 1413 1413 1555 1983 1555 18401983 1555 rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm,rpm, rpm, rpm, rpm, 11 115 70 112 22 75 100 95 70 113 38 110 114 72 6651 ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lbft-lb ft-lb ft-lb ft-lb ft-lb Stock 0.70 4.73 0.59 0.76 0.64 0.61 0.520.69 0.48 0.63 0.69 0.69 0.65 0.64 0.61 0.74 Coated 0.62 3.39 0.53 0.570.52 0.59 0.59 0.89 0.65 0.71 0.60 0.69 0.67 0.60 0.59 0.69

TABLE 11 NO_(x) Results for Coated Parts and Stock Parts 1840 1840 16981698 2125 2125 1698 2268 1413 1413 1555 1983 1555 1840 1983 1555 rpm,rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm, rpm,rpm, 11 115 70 112 22 75 100 95 70 113 38 110 114 72 66 51 ft-lb ft-lbft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lb ft-lbft-lb ft-lb Stock 511 696 2323 2914 123 2023 2369 1823 1490 1803 29333432 2702 3876 3165 3206 Coated 182 704 1624 2033 104 1653 1776 1484 840776 1955 2343 1485 2760 2099 2046

Example 9 Friction Reduction

Three aluminum alloy panels were selected for friction comparisons:

-   -   a panel having a titanium dioxide coating as-deposited per        Example 1;    -   a panel having a titanium dioxide coating as-deposited per        Example 1 and subsequently polished using fine grain abrasive of        less than 300 grit and    -   as a benchmark, a panel coated with a commercially available        diamond like carbon coating (DLC) used in coating metal        substrates for high performance, low friction applications.        Each panel was subjected to friction testing per ASTM        1894 (2008) procedure with the test panel sample as the sled and        a 4×12 iron substrate as the mating surface. The test results        are shown in the table below.

TABLE 12 Coating Static Friction Dynamic Friction Titanium Dioxide0.3925 0.3786 Coating Unpolished Titanium Dioxide 0.1991 0.1948 Coatingpolished Diamond like carbon 0.2039 0.2003 coating (DLC)The above test results show that the polished titanium dioxide coatinghas coefficient of friction equal to or better than the commerciallyavailable coating both in static and dynamic friction tests.

Example 10 Doping of Titania Coating

Five aluminum alloy cylinder heads for a four stroke gasoline internalcombustion engine were selected for dopant testing. One cylinder headwas left uncoated. A second cylinder was coated according to theinvention with titania coating. A third cylinder head was coatedaccording to the invention with the addition of 10 g/l cobalt carbonatedissolved in the electrolyte. The fourth cylinder head, after coatingwith titania coating and drying, was burnished with 50 nanometer Ptpowder. This nanoparticulate powder was rubbed into the dried titaniacoating using a wool polishing wheel resulting in deposition in thepores and on surface of the titania of about 0.2 grams of 50 nanometerPt powder. A fifth cylinder head was coated according to the inventionwith the addition of 10 g/l sodium ammonium decavanadate dissolved inthe electrolyte.

The coated cylinder heads were assembled and tested serially, meaningone after the other sequentially in time, into the same four strokeengine, which did not have a catalytic converter attached. With eachcoated cylinder head, the engine was operated at various RPMs, under 80to 100 percent load, and varied air/fuel ratios as shown in FIG. 6 a-6d. Emissions were tested downstream of the combustion chamber at eachengine operating parameter, for each coated cylinder head. Test resultsshowed reduction in NO_(x) emissions at lean, stoichiometric and richfuel mixtures can be achieved by addition of vanadium to the titaniumdioxide coating.

Although the invention has been described with particular reference tospecific examples, it is understood that modifications are contemplated.Variations and additional embodiments of the invention described hereinwill be apparent to those skilled in the art without departing from thescope of the invention as defined in the claims to follow. The scope ofthe invention is limited only by the breadth of the appended claims.

1. A method to reduce emissions from an apparatus comprising anoperating internal combustion engine, said internal combustion enginecomprising a combustion chamber, an air-intake valve and an exhaust gasvalve; the method comprising depositing a chemically adherent titaniumdioxide containing coating on a portion of aluminum surfaces of at leastone of: a portion of surfaces defining the combustion chamber; aninternal surface of an air-intake passage in communication with thecombustion chamber via an air-intake port that is opened and dosed bythe intake valve; an internal surface of an exhaust emission passage incommunication with the combustion chamber via an exhaust gas valvethrough an exhaust gas port; the air-intake valve; the exhaust gasvalve; and an exhaust manifold in communication with the exhaustemission passage; such that, during operation of said engine, intakeair, fuel/air mixture and/or exhaust gas contact said coating therebyincreasing decomposition rate of HC, CO or NO_(x) and/or reducingformation rate of CO or NO_(x) emissions resulting from combustion inthe combustion chamber.
 2. A method to reduce emissions from anoperating internal combustion engine, comprising the steps of:determining a state of an engine operating parameter corresponding to anemission value of at least one of HC, CO and NO_(x) emitted from acombustion chamber of an operating internal combustion engine,determining a target reduction in concentration of at least one of HC,CO and NO_(x) in exhaust gas discharged from the operating internalcombustion engine corresponding to the state of the engine operatingparameter corresponding to the emission value of at least one of HC, COand NO_(x) emitted from the combustion chamber of the operating internalcombustion engine, wherein the concentration of the at least one of HC,CO and NO_(x) is measured at a selected location in a path of theexhaust gas that is downstream from the combustion chamber; anddepositing a chemically adherent titanium dioxide containing coating ona portion of surfaces of a. the combustion chamber; b. an air-intakepassage in communication with the combustion chamber; c. an exhaustpassage in communication with the combustion chamber; d. Intake and/orexhaust valves; and/or e. an exhaust manifold in communication with theexhaust passage; to effect said target reduction in concentration of atleast one of HC, CO and NO_(x) in exhaust gas discharged from theoperating internal combustion engine. 3.-12. (canceled)
 13. An internalcombustion engine comprising: external surfaces and internal surfaces,said internal surfaces comprising a group of internal surfaces locatedon at least one of a combustion chamber, an air intake passage, anexhaust passage, an exhaust manifold, a valve and combinations thereof;at least a portion of said group of internal surfaces being metalselected from aluminum, aluminum alloy, titanium or titanium alloy; andat least some portions of the metal being coated metal surfaces having achemically adherent coating comprising TiO₂, said coated metal surfacespositioned such that, during operation of said engine, intake air,fuel/air mixture and/or exhaust gas contact said chemically adherentcoating thereby increasing decomposition rate of HC, CO or NO_(x) and/orreducing formation rate of CO or NO_(x) emissions resulting fromcombustion in the combustion chamber.
 14. The engine of claim 13 furthercomprising an exhaust system extending from the exhaust manifold to anexhaust pipe wherein at least a portion of internal surfaces of theexhaust system being aluminum, aluminum alloy, titanium or titaniumalloy coated with said chemically adherent coating. 15.-18. (canceled)19. The method according to claim 1, comprising applying the coating toat least one of a bowl surface of a piston, a crown surface of a piston.20. The method according to claim 1, comprising applying the coating totop surfaces of the intake and exhaust valves.
 21. The method accordingto claim 1, comprising applying the coating to a surface of a cylinderhead exposed to the combustion chamber.
 22. The method according toclaim 1, comprising applying the coating to a surface of walls of acylinder and/or a cylinder liner.
 23. The method according to claim 1,further comprising a dopant in and/or on the chemically adherenttitanium dioxide containing coating.
 24. The method according to claim1, wherein determining a state of an engine operating parametercorresponding to an emission value of at least one of HC, CO and NO_(x)emitted from a combustion chamber of an operating internal combustionengine, comprises determining engine speed of the internal combustionengine operating at steady state engine temperature.
 25. The methodaccording to claim 1, wherein determining a state of an engine operatingparameter corresponding to an emission value of at least one of HC, COand NO_(x) emitted from a combustion chamber of an operating internalcombustion engine, comprises determining engine exhaust gasrecirculation (EGR) values of the internal combustion engine operatingat steady state engine temperature.
 26. The method according to claim 1,wherein determining a state of an engine operating parametercorresponding to an emission value of at least one of HC, CO and NO_(x)emitted from a combustion chamber of an operating internal combustionengine, comprises determining engine load or torque of the internalcombustion engine operating at steady state engine temperature.
 27. Themethod according to claim 1, wherein determining a state of an engineoperating parameter corresponding to an emission value of at least oneof HC, CO and NO_(x) emitted from a combustion chamber of an operatinginternal combustion engine, comprises determining engine indicated meaneffective pressure (IMEP) of the internal combustion engine operating atsteady state engine temperature.
 28. The engine according to claim 13comprising a combustion chamber having at least one aluminum, aluminumalloy, titanium or titanium alloy surface, at least a portion of saidsurface having deposited thereon a coating comprising at least 25 wt %TiO₂ in a layer thickness such that during operation of said engineexhaust gas emissions of HC, CO and/or NO_(x) from the combustionchamber are less than said emissions from a like engine having notitanium dioxide coating on combustion chamber surfaces.
 29. The engineaccording to claim 13, wherein the coated metal surfaces having achemically adherent coating comprising TiO₂ are polished surfaces havingan Ra of 0.01 to 1.0 micron.
 30. The engine according to claim 13,further comprising a dopant in and/or on the chemically adherent coatingcomprising TiO₂.